The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An electric-powered induction motor transforms electric power to mechanical power by inducing rotating magnetic fields between a static element, i.e., a stator, and a rotatable element, i.e., a rotor. The rotating magnetic fields generate torque on a shaft of the rotor through conductor bars. Known stators can induce current flows through conductor bars on the rotor that may be parallel to an axis of the motor.
A known rotor for an induction motor includes a stack of steel sheets assembled onto a rotatable shaft, and a plurality of conductor bars fabricated from conductive material, e.g., copper or aluminum. The conductor bars are preferably connected at both axial ends of the rotors using shorting rings.
Known rotor fabrication methods include assembling the laminated steel stack and molding shorting rings and conductor bars on an outer periphery of the rotor. This includes placing the laminated steel stack into a casting mold, e.g., a die cast mold having a plurality of casting cavities. Molten material is introduced into open spaces formed in the rotor and open spaces between the die cast mold and the laminated steel stack to form the shorting rings and conductor bars.
It is known that oxide inclusions and voids can be formed in the conductor bars and shorting end rings during mold filling of molten material and solidification. Molten material may be introduced into the mold at single or multiple locations. For example, in high pressure die casting process, molten material is injected under pressure though open slots formed in the laminated steel stack, e.g., a plurality of conductor bar grooves, and flows to open spaces between the die cast mold and ends of the laminated steel stack to form shorting end rings. The molten material injected into the die casting mold flows from a relatively large volume occurring at the first shorting end ring through the plurality of conductor bar grooves and to the second, remote shorting end ring. The molten material can cool and partially solidify during turbulent flow of the molten material into the plurality of conductor bar grooves due in part to exposure to surface areas of the conductor bar grooves. The partially solidified molten material may impede molten material flow and cause voids, oxide inclusions, and other discontinuities in the conductor bars and the shorting end rings.
Power density output from an electric induction motor correlates to quality of the conductor bars, and mass bulk density of the individual conductor bars. It is known that voids formed in the conductor bars and the shorting end rings during fabrication reduce power density output of the electric induction motor. The presence of oxide inclusions and cracks due to hot tearing reduces the electric conductivity of the conductor bars and shorting end rings.